Investigation on short circuit severity for Li-ion batteries under mechanical abuses and its empiric model development

The increase of CO2 emissions and the threat of global warming is leading to find technological solutions to reduce the greenhouse gases. Since the usage of fossil fuels for mobility produces a significant slice of CO2 emissions, the electric-mobility represents an alternative solution with lower CO2 impact. However, electric vehicles must guarantee safety requirements in order to make the public opinion feel confident towards this new technology. Consequently, compulsory tests defined by international standards (GTR20) must be performed on the EVs (Electrical Vehicles) components, before launching them on the market. Therefore, since performing tests is time and money consuming, it is beneficial to develop simulation models - based on the evaluation of some specified parameters - able to predict if a newly proposed design can be either accepted or rejected. This is called simulation-design loop and its target is the improvement of performances (ex. driving range) withstanding the safety requirements. With simulation models, the number of needed tests can be sensibly reduced having a beneficial impact on costs and time. In this work an empirical multi-physics numerical model has been developed, with the purpose to predict the voltage distribution, the electric current and the temperature of a Li-ion battery in case of electrical short circuit or nail penetration. Simulations have been validated with experimental tests. The battery under analysis - obtained by disassembling the battery pack of a commercial vehicle - is a laminate pouch-type cell, composed by Graphite as anode material, a spinel of NMC and LMO as Cathode material. The cell showed a rated capacity of 41 Ah and a nominal voltage of 3.7 V. The correct evaluation of these parameters allows to tell in advance if the tested cell will incur in a thermal runaway. The obtained model can be employed for a preliminary study of the thermal propagation on the newly designed cells.